This invention relates to the disposal of polychlorinated biphenyls, commonly known as PCBs. More particularly, this invention relates to processes for the detoxification of soils, sludges and sediments by degradation of PCBs contained therein into environmentally and toxicologically harmless compounds. Even more specifically this invention relates to methods for remediation of soils in an economically and technically advantageous method.
In their most common form, PCBs are mixtures of isomers of trichlorobiphenyl, tetrachlorobiphenyl, pentachlorobiphenyl, and small amounts of dichlorobiphenyl and hexachlorobiphenyl. Up until the early 1970's PCBs were used in a wide range of applications due to their unique blend of fire resistance, thermal and oxidative stability, electrical characteristics, solvency, inertness and liquid range. Some of their most important uses were as follows: as a dielectric medium in transformers, either alone or in blends with other materials such as trichlorobenzene; as the dielectric impregnating medium in capacitors; as plasticizers; as ingredients in lacquers, paints and varnishes and adhesives; as water proofing compounds in various types of coatings; as lubricants or lubricant additives under extreme conditions; as heat transfer fluids; as fire resistent hydraulic fluids; as vacuum pump fluids; and as air compressor lubricants. Their largest application was in the electrical industry as a dielectric medium in transformers and capacitors.
In the late '60's and early '70's, it was discovered that PCBs have a major potential for environmental contamination due to their extremely slow biodegradation rates. The persistence and toxicity of PCBs have prompted governmental action restricting their use and application, and the Toxic Substance Control Act of 1976 contained provisions for discontinuance of their use and for their eventual disposal. Even trace amounts of PCBs are considered undesirable.
Current regulations issued by the Environmental Protection Agency specify incineration as the only acceptable method of PCB disposal in the absence of special clearance. Incineration, of course, is expensive and hazardous, and in cases where the PCBs are a minor component mixed in with a nonprohibited fluid such as one of the various types of replacement dielectric fluids, one loses the nonprohibited fluid as well by incinerating the entire mixture.
Methods for remediating soils, sediments and sludges include incineration, solvent extraction, chemical treatment and other processes. Each of these prior art methods has its drawbacks and the art has sought new and better methods for destroying toxic PCBs in soils, sediments and sludges.